Implantable medical devices (IMD) that can alert patients or third parties to the detection of ischemic events including heart attacks (Myocardial Infarction) can save lives and reduce damage to a patient's heart tissue, improving the post-myocardial-infarction quality of life. Myocardial infarction (MI) occurs when a blood clot blocks the blood supply to a portion of the heart causing the heart tissue to become hypoxic (ischemic) and also experience decreased metabolite removal. Ischemia detection may occur by analysis of the patient's cardiac activity, especially via electrical waveforms sensed by electrodes.
The combination of a pacemaker or ICD with an ischemia detector is described by Fischell et al in U.S. Pat. Nos. 6,112,116, 6,272,379 and 6,609,023. Fischell describes an IMD which can detect a change in the electrical signal from the patient's heart (cardiac electrical signal) that is indicative of a cardiac event, such as an acute ischemia, and then provide a notification of such an event. The IMD can also be a medical device which senses and/or stimulates cardiac, neural, vagal-nerve, or other anatomical target in order to control cardiac activity. Fischell also describes an external alarm system that can provide additional visual, sonic and vibratory alerting signals and may also provide voice/data communication between the IMD and a remote medical monitoring station.
Fischell et all in the above mentioned patents primarily uses changes in the ST segment of the electrogram as the primary indicator of ischemia. Unfortunately, the intracardiac electrogram seen during episodes of left bundle branch block (LBBB) often exhibit significant ST changes that could be misinterpreted as an ischemic event. A helpful characteristic of the LBBB electrogram signal is a significant widening of the QRS complex. Fischell et al do not describe a specific scheme for performing ischemia detection in a patient that experiences both normal and LBBB beats.